It is proposed to continue ongoing studies of neurite regeneration and specificity of synapse formation between nerve cells. A detailed understanding of these and related phenomena will be essential for extending knowledge about normal and abnormal development, and for devising strategies to help patients recover function following injury to the nervous system. The system of large identifiable Aplysia neurons in primary cell culture will be used to examine synaptic specificity and synaptic plasticity. These neurons regenerate neurites and form specific electrical and chemical synapses in culture, and it has been found that the patterns of growth and specificity can be changed by adding the lectin Concanavalin A to the culture medium. Thus, although Concanavalin A itself is unlikely to be involved in neuronal development, it can be used as a tool to investigate fundamental problems in synaptogenesis. It is proposed now to build on these findings and ask questions about the molecular mechanisms of action of Concanavalin A, using a combination of electrophysiological, biochemical and molecular biological approaches. The long term goal of these multidisciplinary studies is to understand the molecular basis of synaptic specificity and synaptic plasticity, phenomena which are essential for the proper functioning of the nervous system.